The purpose of a bearing protector is to prevent the ingress of fluid, solids and/or debris from entering a bearing chamber. Equally, bearing protectors are employed to prevent the egress of fluid or solids from a bearing chamber. Essentially, their purpose is to prevent the premature failure of the bearing.
Bearing protectors generally fall into two categories: repeller or labyrinth bearing protectors; and mechanical seal bearing protectors. Reference is made to our co-pending mechanical seal bearing protection application WO-A-2004005770, which discloses a substantially contacting bearing protector.
A labyrinth bearing protector typically includes a component which is mounted for rotation about a shaft and axially fixed in relation thereto. For example, the shaft may be that of a pump or other piece of rotating equipment. The protector includes a static component which is also axially fixed and is butted or secured to the stationary part of the equipment.
The rotating component typically has a complex outer profile which is located adjacent and in close radial and axial proximity to a complex inner profile of the stationary component. Together these complex profiles, in theory, provide a tortuous path preventing the passage of the unwanted materials or fluids.
A labyrinth bearing protector normally works only during the operation of the equipment. This is because the design relies on the counter rotation of the rotary and stationary component to create centrifugal forces, which discourage the passage of fluid radially between such components.
When the equipment is static, the complex labyrinth design is unable to hold a fluid level which, in horizontal application, is at a higher radial level than the inlet position of the protector.
Furthermore, in many industrial applications, water spray, steam and foreign contaminants are directed at the bearing protector when the equipment is static. Traditional labyrinth designs are unable to prevent the entry of such contaminants into the bearing chamber.
Also, bearing chamber breathing is a further industrial field problem. During operation the lubrication fluid and air in the bearing chamber expand as it warms. In a traditional labyrinth seal arrangement this expansion will expel air through the labyrinth and “breath” out of the bearing chamber. Once the equipment stops, the bearing chamber cools and the air inside contracts, sucking moist air past the labyrinth arrangement and back into the bearing chamber. This is referred to as “breathing” in.
A mechanical seal bearing protector can overcome the static limitations of the labyrinth design. However, these devices can suffer from other problems such as excessive heat generation in high shaft speed applications or when there is marginal or no lubrication at the seal faces. Therefore the use of mechanical seal bearing protectors is limited.
There is a need for a non-contacting labyrinth-type seal bearing protector which can seal fluids when the equipment is stationary and/or can prevent and/or reduce the volume of air-born molecules entering the bearing chamber during chamber breathing.
It would also be of advantage if a non-contacting labyrinth-type seal could repel fluid irrespective of the direction of shaft rotation. This reduces the likelihood or effect of installation error.
It could be of further advantage if a non-contacting labyrinth-type seal incorporates two repelling devices, one designed to repel fluid from escaping the bearing chamber and one designed to repel fluid from entering the bearing chamber.
Furthermore, installation ease is important with all bearing protector designs. A non-contacting labyrinth-type seal which is very axially compact is desirable so that it may be fitted into spaces previously occupied by lip seals and supplied in a one piece cartridge unit with no setting clips.
U.S. Pat. No. 5,378,000 (Orlowski) discloses a cartridge design having a labyrinth configuration in which the rotor and stator are locked together axially by a solid deformable annular seal or an elastomer. The elastomer is locked between two counter-rotating rectangular shaped cavities as illustrated in FIGS. 3 and 4 of Orlowski. The elastomer is subject to frictional resistance, less by the stator and more by the rotor. The elastomer in Orlowski therefore suffers from frictional wear between the two counter-rotating bodies. This frictional wear is exacerbated by the following:                The acute angle between surfaces 23 and 22b of the rotor 14 and the 90 degrees angle of the three remaining corners of grooves 21 and 22, which come into contact with the elastomer (20). Orlowski relies on the relatively un-chamfered surfaces of these four points in contact with the elastomer, so to maintain axial proximity between the rotor and stator.        All commercially available elastomers have a cross-sectional size tolerance. This is typically +/−3% of their nominal diameter. The magnitude of Orlowski's defined frictional resistance, is therefore highly variable given this elastomer tolerance and the fact that grooves 21 and 22 will have an associated manufacturing width tolerance also.        During assembly of the seal onto the equipment, the device is axially pulled and pushed as it is moved into its final running position. This axial displacement is particularly due to the frictional drag forces from the rotary elastomer 15 and the shaft 10. This axial displacement places the elastomer 20 under shear forces since it is this elastomer which is the only element axially locking the rotor and stator together. It is therefore highly probable that the frictional resistance between the elastomer and the sides of grooves 21 and 22 will change during assembly.        
All of these facts influence and rapidly increase the wear on the elastomer 20 and as such limit the elastomers useful sealing life against the ingress or egress of matter.